Motor controller system for battery-powered motors

ABSTRACT

A motor controller system ( 15   a ) for dc power source motors ( 10 ) which includes a sensor device ( 16 ) that operates to measure and generate a voltage signal from the motor current and the rate of change of said current, and a programmable input/output processor ( 12 ) which receives voltage signals as input from the motor current, dc power source ( 11 ) and/or motor ( 10 ) and compares on or more of these voltage signals to one or more control parameters. Based upon these comparisons, the processor ( 12 ) generates a pulse width modulation control signal, which triggers a switching mechanism ( 14 ) and related interrupt service routing to make adjustments to the operational parameters of the motor by periodic interruption of the motor current.

FIELD OF THE INVENTION

[0001] This invention relates to a motor controller system forbattery-powered motors which measures the impact of loads on a motor andits battery at specific instances and, through application of analgorithm and related control parameters, calculates the necessaryadjustments to motor speed and torque and corresponding battery use tomaximize motor efficiency and extend battery life.

BACKGROUND OF THE INVENTION

[0002] Many battery-operated appliances and small vehicles are beingmarketed today in place of those powered manually or by a small internalcombustion engine, which is inefficient and produces a high level ofemissions. Lawn mowers, power garden tools, other power tools, bicycles,wheel chairs and golf carts are among such examples. These devices andvehicles are typically driven by a brushed direct current (“dc”) motor,which is directly connected with a lead-acid rechargeable batterythrough a simple on/off switch. Typically, no means of power control isprovided. As a result, the motor runs at high speeds when the battery isfully charged, wasting the battery power. As the battery is drained, themotor voltage drops and the motor speed decreases below the optimaloperating speed, causing inefficiency in battery use. As part of thisprocess, the battery may be drained to a low voltage level which causesan irrecoverable damage to the battery. Further, such motors have nomeans of adjusting power and speed in response to various load factors,which causes further inefficiencies in motor and battery usage betweencharges. Battery management systems have been developed for low powersystems such as laptop computers and wireless phones. Also, variouscontrol schemes are implemented for electric and hybrid electricvehicles that employ traction motors of tens of kilowatts or higher.However, an inexpensive battery-powered control system that handlespower in the range of several hundred watts and further takes intoaccount of the characteristics of the power loads has not beenavailable. Applications for such a battery-powered control systeminclude: (a) an electric bicycle, (b) an electric vehicle, (c) a hybridelectric vehicle, (d) a three-wheeler (electric), (e) a hybridthree-wheeler, (f) a battery-operated lawn mower, (g) a battery operatedgolf cart, (h) a battery-operated wheel chair, (i) a battery-operatedgo-cart, and (j) battery-operated garden or power tools.

[0003] For example, battery-operated lawn mowers are currently marketedwhich employ no means of motor control as disclosed by the presentinvention. Various load factors impact on the operation of the motor andbattery, including condition of the grass and the speed at which themower is pushed. Without a means to compensate for the impact of theseload factors, motor efficiency and battery life are negatively effected.

[0004] Similarly, an electric bicycle will experience load or drains onits battery in connection with the power necessary to overcome (a)rolling resistance, (b) drag resistance and (c) climbing resistance.Additionally, power is needed, and corresponding motor/battery loadresults in connection with acceleration of the bicycle. Finally, powercan be added to a bicycle through human assistance and also fromregenerative braking which can also add power to the motor/batterysystem. No system currently exists which measures each of these factorsand provides corresponding control to the motor and battery system.

OBJECT OF THE INVENTION

[0005] Accordingly, it is the object of the present invention to providean inexpensive means for controlling a battery-operated dc-motor systemto promote motor efficiency and extend battery life. More specifically,the present invention provides a novel motor controller system forbattery-powered motors which measures the impact of loads on a motor andits battery at specific instances and, through application of analgorithm and related control parameters, calculates the necessaryadjustments to motor speed and torque and corresponding battery use tomaximize motor efficiency and extend battery life.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] A better understanding of the present invention can be obtainedwhen the following detailed description of the preferred embodiment isconsidered in conjunction with the following drawings, in which:

[0007]FIG. 1 is a graph showing the performance characteristics of abattery-powered electric lawn mower;

[0008]FIG. 2 is a graph showing the expected battery life that can beachieved for an electric lawn mower run at various blade speeds; and

[0009]FIG. 3 is a block diagram of an embodiment of the motor controllersystem of the present invention.

[0010] While the invention is susceptible to various modifications andalternative forms, specific embodiments thereof are shown by way ofexample in the drawings and will herein be described in detail. Itshould be understood, however, that the drawings and detaileddescription below are not intended to limit the invention to theparticular form disclosed, but on the contrary, the invention is tocover all modifications, equivalents and alternatives falling within thespirit and scope of the present invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0011] In a preferred embodiment of the present invention, a motorcontroller system is provided for use with a battery-operated dc-motorsystem, which motor controller system measures the impact of variousloads that may be exerted upon a motor and battery and, throughapplication of algorithm and related control parameters programmed orotherwise input into an input/output microprocessor, automaticallyadjusts the power being provided to the motor by the battery. By usingthe algorithm and related control parameters, the motor controllersystem, through its microprocessor, determines the power necessary toperform a particular task at a given time. Thus, the battery life may beextended, in some instances, by as much as two to four times, incomparison to a motor that is connected to a battery through a simpleon/off switch.

[0012] As set forth above, the motor controller system of the presentinvention has application to motor/battery systems in the range ofseveral hundred watts and include, but are not limited to: (a) anelectric bicycle, (b) an electric vehicle, (c) a hybrid electricvehicle, (d) a three-wheeler (electric), (e) a hybrid three-wheeler; (f)a battery-operated lawn mower, (g) a battery-operated golf cart, (h) abattery operated wheel chair, (i) a battery-operated go-cart and (j)battery-operated garden or power tools.

[0013] In the case of a battery-operated lawn mower, in particular, FIG.1 demonstrates the benefits that can be achieved through the use ofmotor controller. FIG. 1 reveals the performance characteristics of aBlack and Decker battery-operated lawn mower with the followingspecifications: Power ˜500 watts Cutting Width 19″ Cutting Height 1½-3⅓″Weight 76 lbs. Battery 24 V, 413 Wh (two 17.2 Ah batteries in series)

[0014] In this context, blade speed was set at 600, 1200, 1800, 2400,3000 and 3600 rpm, and associated power loss to run the motor and itsbreakdowns, namely, air drag loss, iron loss and copper loss (Jouleheating loss) were measured and are estimated as set forth in FIG. 1.

[0015] Also shown in FIG. 1 is estimated power required to mow the lawn.Notably, where blade speed can be controlled at 1200 rpm, a significantportion of the motor power (nearly two thirds) is committed tograss-cutting work. Grass-cutting work stays relatively constant acrossall blade speeds and, at higher blade speeds, in comparison, most motorpower contributes to compensation for the load impacted by air drag.

[0016] The current and battery life associated with operations of thelawn mower at the various blade speeds outlined above are summarized inFIG. 2.

[0017] Battery life is longest when blade speed is controlled at 1200rpm because the required power is lowest when the mower is operated atthis speed.

[0018] In general terms, the motor controller of the present inventionmeasures the impact of various loads on a motor and its battery inparticular applications and, through use of microprocessor andassociated algorithm, provides only the necessary and sufficient powerneeded to carry out a given task. The motor controller essentiallyconsists of three components: (1) means of measuring and convertingmotor current to a voltage signal, (2) a microprocessor which (i)receives and analyzes this motor control voltage signal, as well asbattery voltage and/or motor voltage signals, (ii) calculates an optimalcontrol parameter for the associated motor based on this voltage signalanalysis and (iii) outputs an associated control signal, and (3) adevice which, based upon this control signal, adjusts the motor currentand/or voltage to obtain desired operational parameters for the motor.

[0019] Analysis of current and voltage is important because theseparameters of motor operation help measure motor speed and torque. Morespecifically, in dc-motors, torque is proportional to motor current;thus, speed and torque characteristics of a motor can be determined ifcurrent and voltage are known. The magnitude of motor current can bedetermined by measuring the voltage across a resistor of known valuewhich is connected in series with the motor winding. Alternatively,current may be measured by a current sensing device that measures themagnetic fields around the current carrying conductor. When a constantvoltage is applied to the motor, its speed can be measured by detectingthe voltage change associated with switching of the brush of the motor.Alternatively, motor speed can be calculated from motor voltage andmeasured motor current. Motor voltage can also be determined by dividingthe voltage across the motor winding with an appropriate resistornetwork and a filtering circuit. dc motors generally produce a devoltage proportional to the rotational speed of the motor. This voltageis referred as back-emf (electromotive force). Motor voltage is asummation of the back-emf, resistive loss in the coil winding (copperloss) and hysteretic and inductive loss associated with the magneticcircuit of the motor (iron loss). In addition, inductance of the coilwinding produces an additional voltage that is proportional to the rateof change in the current. Among these factors, the inductance relatedterm and the resistive term can be subtracted from the measured motorvoltage (Vm) by measuring the current and its rate of change. Theremaining terms that are related with back-emf and iron loss are bothproportional to the speed of the motor. Thus, once the proportionalityconstant is determined for a given motor, its speed can be calculated.

[0020] Calculation of an optimal control parameter involves use of amicroprocessor and associated algorithm which receives as input themeasured current as a converted voltage signal, the voltage (and relatedvoltage signal) produced by the battery (or other dc power source)and/or the motor voltage (and the related voltage signal). Themicroprocessor then compares one of more of such voltage signals to oneor more control parameters and, based upon such measurement, sends oneor more control signals to make necessary adjustments to the motor andbattery power. In a preferred embodiment, the primary control parameteris the duty cycle of a pulse width modulation (pwm) signal.

[0021] In particular, the microprocessor can control motor speed andvoltage by pulse width modulation technique. More specifically, thecurrent to the motor can be interrupted periodically by a switchingmechanism such as a semiconductor switch, e.g., a bipolar transistor, ametal oxide field effect transistor (MOSFET) or an insulated gatebipolar transistor (IGBT).

[0022]FIG. 3 shows a block diagram of a preferred embodiment of thepresent invention which implements the above-described components. InFIG. 3, a motor 10 and a battery 11 form a circuit with a current 15.When a switch 14 is closed, a current path 15 a completes a return pathto battery 11. Motor 10 can be, for example, a brushed dc permanentmagnet motor.

[0023] In a preferred embodiment of the present invention, the circuitformed by motor 10 and battery 11 further includes, as part of a motorcontroller system 30 of the present invention, an electronic(semiconductor) switch 14, a current sensor device 16 and a protectivediode 17. Outside of the circuit, the motor controller system 30 of thepresent invention, in a preferred embodiment, also includes amicroprocessor 12, a driver 13 and signal conditioners 18, 19 and 20.

[0024] In operation, the motor controller system 30 receives as inputthe current 15, a motor voltage signal 22 and/or a battery voltagesignal 21. In a preferred embodiment, current 15, as well as the rate ofchange of current 15, is detected and measured by current sensor device16, which generates a corresponding voltage signal 23 for input intomicroprocessor 12. Measurement of current 15 by current sensor device 16can be accomplished through use of a resistor (e.g. a 0.005 ohm powerresistor) which is connected in series with the motor winding of motor10. The corresponding voltage across this resistor can be amplified by adifferential amplifier to give voltage signal 23. (This resistor andamplifier, together, comprise the current sensor device 16.)Alternatively, the current 15 can be determined by measuring themagnetic field associated with the current using a magnetic fieldsensing device such as a Hall sensor chip that outputs a correspondingvoltage signal 23. (The Hall sensor chip is essentially the currentsensor device 16 in this alternative embodiment.) Once again, currentsensor device 16, based upon this measurement, outputs a correspondingvoltage signal 23. For battery voltage 21, a voltage divider deviceassociated with battery 11 may be used in a preferred embodiment togenerate battery voltage 21 and a related voltage signal, although othermeans of generating a battery voltage signal may also be employed. Thisbattery or dc power source detection function is incorporated intosignal conditioner 18. Motor voltage and a related voltage signal 22 canbe generated, for example, by employing a differential amplifier and anappropriate R-C filter. Again, other means of generating a motor voltagemay be used. This motor voltage detection function is incorporated intosignal conditioner 19. Notably, input of the motor voltage signal 22 maybe omitted in motor controller system 30 because motor voltage otherwisecan be calculated, by the processor, from the input of battery voltage,motor current and the rate of change in the motor current.

[0025] After the current signal 15 is converted into voltage signal 23,voltage signal 23 can be conditioned by signal conditioner 20. In apreferred embodiment, signal conditioner 20 filters voltage signal 23through use of an R-C filter with a time constant of a few millisecondsin order to filter out rapid changes in voltage caused by pulse widthmodulation as well as the motor brush noise. The filter time constant isselected so that the filtered signal 23 is still responsive to thechanges in the current 15 that are caused by the changes in motor speedand torque. Similar signal conditioners 18 and 19, employingappropriately designed resistor networks and R-C filter circuits, may beimplemented for the conditioning of the battery voltage signal 21 andthe motor voltage signal 22, respectively.

[0026] Microprocessor 12 can receive voltage signals 21, 22 and 23,after conditioning by signal conditioners 18, 19 and 20, respectivelyvia analog-to-digital (A/D) input ports. (Again, input of motor voltagesignal 22 can be omitted.) In a preferred embodiment, microprocessor 12is a programmable input/output processor such as a Motorola®MC68HC705MC4. As discussed more fully below in the context of possiblecontrol strategies, microprocessor 12 can compare one or more of voltagesignals 21, 22 and 23 to corresponding control parameter, i.e., desiredbattery voltage, motor speed or motor torque operational parameters,and, based upon such comparison, generates a control signal 24 to driver13. Driver 13, in turn, controls a gate of electronic switch 14. In apreferred embodiment, microprocessor 12 provides a pulse widthmodulation signal with a controlled duty cycle to driver 13. Asdiscussed above, in a preferred embodiment, the current to the motor canbe interrupted periodically by a switch 14 such as a semiconductorswitch, e.g., a bipolar transistor, a metal oxide field effecttransistor (MOSFET) or an insulated gate bipolar transistor (IGBT).

[0027] In connection with switch 14, a protection diode 17 is placed inparallel to motor 10 along current path 15 b. Typically, motor 10 hassizable inductance, such that current 15 will only slowly dissipate whenswitch 14 is open. As a result, the current 15 will quickly charge upany stray capacitance resulting in a very high voltage that can damageor destroy electronic switch 14. Protection diode 17 and related currentpath 15 b provide an alternative current path when switch 14 is openand, thereby, prevent damage and possible destruction of switch 14. Itis important that current sensor device 16 is also placed in parallel toprotection diode 17, i.e., the current sensor device 16 is placed nextto and in series with motor 10 before the current 15 branches toprotection diode 17. Otherwise, the current sensor device 16 will bemeasuring the average current draw from the battery 11.

[0028] In a preferred embodiment, operator input to microprocessor 12can adjust the control parameters associated with the input voltagesignals for motor current, battery voltage and/or motor voltage.Operator input can also adjust the control strategies implementedthrough the motor control system, as are set forth more fully below. Inall cases, measurement, calculation and control routine is implementedas an interrupt service routine that is triggered by the pulse widthmodulation signal. This synchronization with the pulse width modulationsignal is needed because the pulse width modulation causes a largevoltage fluctuation as the current to the motor is turned on and off. Inorder to minimize the error caused by the voltage fluctuation, thevoltage is measured with a certain delay after the switching. When allthe necessary measurements and calculations cannot be completed in asingle pulse width modulation cycle, such a task may be divided intosmaller tasks so that each divided task can be completed with one pulsewidth modulation cycle. Such a routine may be executed either during theon-period or the off-period of the pulse width modulation cycle. Inorder to ensure its completion, it may be selected to execute during thelonger of the periods depending on the duty cycle of the pulse widthmodulation signal.

[0029] In accordance with the preferred embodiment of the currentinvention, the following three control strategies can be implemented:

[0030] Constant voltage output—This strategy is selected when constantvoltage operation over the battery life is desired. The microprocessormonitors the battery voltage (Vb) and a control signal that indicatesthe desired output voltage (Vo). The control voltage may be provided bymeans of an analog voltage signal that is measured by the microprocessorthrough its analog-to-digital converter. Alternatively, it may be sentto the microprocessor as a digital signal via its serial data interfaceor its digital input port. The microprocessor periodically calculatesthe ratio (x) of Vo to Vb and sets the duty cycle of the power widthmodulation to this ratio.

[0031] Constant speed—With the present invention, an approximateconstant speed operation may be achieved without a use of tachometer orsimilar rotational sensing device. Using a simple relationship thatholds among the motor voltage, current, the rate of change in currentand motor speed, one can calculate the motor speed from the input to themicroprocessor of motor voltage, motor current and rate of change incurrent. Further, the torque of the motor can be determined from thecurrent because the torque is proportional to the current. Constantspeed operation is often desirable to extend the battery life where ahydrodynamic drag and resulting load plays a major role in motoroperation. Measured speed is compared with a desired speed by themicroprocessor which, in turn, adjusts the duty cycle of the pwm signal.The motor controller may be further equipped with a means to modify thedesired speed of the motor. A control knob or selector switch may beadded to the controller so that the user may select a modified speed.The microprocessor reads a voltage signal that is modified by thecontrol knob or selector switch and changes the desired speedaccordingly.

[0032] Constant torque—Constant torque operation is desired, forexample, in traction drives. Traction drives generally demand hightorque for starting from stand still. Direct current (de) motors arewell suited for traction drive because they provide higher torque atlower speed. However, if the start-up torque is not controlled, themotor draws excessive current from the battery at start up. Similar tocontrol of constant speed, constant torque control is possible in thepresent invention because the torque is proportional to the motorcurrent that is measured by the microprocessor. In a typicalapplication, a signal that indicates the desired torque (TO) will besent to the microprocessor either in a form of an analog signal ordigital data. The microprocessor also measures the actual torque fromthe motor (T) and its rate of change. The control parameter will becalculated from these inputs. Various methods can be implemented forthis calculation in order to achieve a smooth and rapid convergence tothe desired torque and its maintenance. For example, the outputparameter can be calculated by multiplying an appropriate constant tothe difference of T0 and T. The calculation formula may also include aterm that repeatedly adds the difference term with a proper scalingfactor so that the output control signal increases if the actual torqueis lower than the target value and decreases if the target value isexceeded. The calculation may further include a term proportional to therate of the change in torque so that the output control value isdecreased if the rate of change is too high. This control method isgenerally known as PID (proportional, integral and differential)control. Other control methods such as fuzzy logic control may beadopted as a main or an alternative control scheme.

[0033] In another preferred embodiment of the present invention, themicroprocessor can also monitor the battery voltage and give a warningto the operator by turning on a light emitting diode (LED) if thebattery voltage becomes lower than a preset value. The warning may alsooccur by other means such as a buzzing sound. If the battery voltagedrops further, the microprocessor can act to turn off the motor current.At the same time, the motor controller can turn on another LED or otherindicator which indicates that the battery is drained.

[0034] Finally, the operational components of the present invention mayalso have application to other dc power sources such as fuel cells andhydroelectric generators. With these power sources, the availablevoltage, current and power may vary significantly. The power controlmethod of the present invention can be adopted in order to maintainsteady performance when motors are driven from such power sources.

What is claimed is:
 1. A motor controller system for dc-powered motorscomprised of a dc power source, a motor and corresponding circuit, saidmotor control system being effective to maximize motor efficiency andextend the life of said dc power source, and comprising: a. a currentsensor device which measures the current of said motor and the rate ofchange of said current and generates a corresponding voltage signal; b.a programmable input/output processor which receives as input saidcurrent sensor voltage signal and a voltage signal from the dc powersource for said motor, compares one or more of said voltage signals toat least one corresponding control parameter, and, based upon saidcomparison, generates a control signal which is comprised of the dutycycle of a pulse width modulation signal; and c. a switching mechanismwhich receives said control signal and, based on said control signal,periodically interrupts said motor current and thereby makes adjustmentsto the operational parameters of said motor, said control signal furthertriggering an interrupt service routine which synchronizes the routineof said current sensor device and processor so that said routines occurafter a fixed delay from completion of the routine of said switchingmechanism.
 2. The motor controller system of claim 1, wherein saidsensor device for said motor current is placed in series with saidmotor, such that said motor is positioned between said switchingmechanism and said motor current sensor device, and said motor and saidmotor current sensor device are in parallel to an additional circuitpath with a protection diode, said protection diode acting to dissipatecurrent and voltage resulting from the inductance of said motor whensaid switching mechanism is open and thereby protect said switchingmechanism from destructive high voltage.
 3. A motor controller systemfor dc-powered motors comprised of a dc power source, a motor andcorresponding circuit, said motor control system being effective tomaximize motor efficiency and extend the life of said dc power source,and comprising: a. a current sensor device which measures the current ofsaid motor and the rate of change of said current and generates acorresponding voltage signal; b. a programmable input/output processorwhich receives as input said current sensor voltage signal and a voltagesignal from the dc power source voltage for said motor, compares one ormore of said voltage signals to at least one corresponding controlparameter, and, based upon said comparison, generates a control signalin the form of the duty cycle of a pulse width modulation signal; c. aswitching mechanism which receives said control signal and, based onsaid control signal, periodically interrupts said motor current andthereby makes adjustments to the operational parameters of said motor,said control signal further triggering an interrupt service routinewhich synchronizes the routine of said current sensor device andprocessor so that said routines occur after a fixed delay fromcompletion of the routine of said switching mechanism; and d. aprotection diode positioned in an additional circuit path parallel toboth said sensor device for said motor current and said motor, saidmotor and said motor current sensor device being placed in series withsaid motor positioned between said switching mechanism and said motorcurrent sensor device, said protection diode acting to dissipate currentand voltage resulting from the inductance of said motor when saidswitching mechanism is open and thereby protect said switching mechanismfrom destructive high voltage.
 4. The motor controller system of claim 1or 3, wherein said switching mechanism is a semiconductor switchselected from the group consisting of a bipolar transistor, a metaloxide semiconductor field effect transistor (MOSFET) and an insulatedgate bipolar transistor (IGBT).
 5. The motor controller system of claim1 or 3, wherein said processor also receives as input and analysis avoltage signal from said motor in generating said control signal.
 6. Themotor controller system of claim 1 or 3, wherein said voltage signalsare conditioned before being input to said processor to filter out anyrapid changes in said voltage signal and any circuit noise caused by theoperation of said motor.
 7. The motor controller system of claim 1 or 3,wherein, in response to operator input, said control parameters can beadjusted.
 8. The motor controller system of claim 1 or 3, wherein, inresponse to operator input, said processor can be adjusted to analyzevoltage signals and generate corresponding control signals which adjustthe operational parameters of said motor in respect to either dc powersource voltage, motor speed or motor torque.
 9. The motor controllersystem of claim 1 or 3, wherein said adjustments to the operationalparameters of said motor are made to obtain substantially constantvoltage output, and said processor: a receives said dc power sourcevoltage signal as input; b. utilizes a control parameter correspondingto a desired dc power source voltage level; c. compares said dc powersource voltage signal with said control voltage by periodicallycalculating the ratio of said dc power source voltage to said controlsignal voltage; and d. generates a control signal based on said ratio.10. The motor controller system of claim 1 or 3, wherein saidadjustments to the operational parameters of said motor are made toobtain substantially constant speed, and said processor: a. receives andutilizes said measurement of said dc power source voltage signal andsaid motor current and motor current rate of change voltage signals asinputs and determines the speed of said motor based on said inputs; b.utilizes a control parameter corresponding to desired motor speed; c.compares said measured motor speed with said control speed; and d.generates a control signal based on said comparison of said measuredmotor speed with said control motor speed.
 11. The motor controllersystem of claim 1 or 3, wherein said adjustments to the operationalparameters of said motor are made to obtain substantially constanttorque, and said processor: a. receives and utilizes said motor currentvoltage signal as input and determines the torque of said motor and therate of change of said torque based on said input; b. utilizes a controlparameter corresponding to desired torque; c. compares said measuredtorque with said control torque; and d. generates a control signal basedon said comparison of said measured torque with said control torque andthe rate of change of said measure torque.
 12. The motor controllersystem of claim 11, wherein said control signal is determined to achievea smooth and rapid convergence to said desired torque operatingparameter by multiplying a constant to the difference between saiddesired torque and said measured torque.
 13. The motor controller systemof claim 1 or 3, wherein said control signal is determined to achieve asmooth and rapid convergence to said desired torque operating parameterby multiplying a constant to the difference between said desired torqueand said measured torque; and said determination of said control signalfurther includes use of a scaling factor which, through the controlsignal, increases torque if said measured torque is less than saiddesired torque and decreases torque if said measured torque is greaterthan said desire torque.
 14. The motor controller system of claim 1 or3, wherein said control signal is determined to achieve a smooth andrapid convergence to said desired torque operating parameter bymultiplying a constant to the difference between said desired torque andsaid measured torque; and said determination of said control signalfurther includes use of a factor proportional to the rate of change insaid measured torque which, through the control signal, adjusts saidmeasured torque downward if said rate of change is too high.
 15. Themotor controller system of claim 1 or 3, wherein said current sensordevice is comprised of a resistor connected in series with the motorwinding of said motor and a differential amplifier.
 16. The motorcontroller system of claim 1 or 3, wherein said current sensor device isa Hall sensor chip.